ABSTRACT
Figure 32.2 M-mode evaluation of normal fetal cardiac rhythm. Top: within the two-dimensional image the reference line is directed through the right atrium (RA) anteriorly and the left ventricle (LV) posteriorly. Bottom: the M-mode display shows the atrial wall movements (open arrows) that precede the ventricular contractions (curved bold arrows). There is a 1:1 relationship between atrial and ventricular activities. The large bars on the time scale show an interval of 1 s; the beat-to-beat interval measures 450 ms which relates to a heart rate of 133 beats per minute.
